U.S. patent application number 15/298154 was filed with the patent office on 2017-02-09 for motor control device and motor control method.
This patent application is currently assigned to Kabushiki Kaisha Yaskawa Denki. The applicant listed for this patent is Kabushiki Kaisha Yaskawa Denki. Invention is credited to Yasuhiko KAKU, Yasufumi YOSHIURA.
Application Number | 20170040916 15/298154 |
Document ID | / |
Family ID | 55652794 |
Filed Date | 2017-02-09 |
United States Patent
Application |
20170040916 |
Kind Code |
A1 |
YOSHIURA; Yasufumi ; et
al. |
February 9, 2017 |
MOTOR CONTROL DEVICE AND MOTOR CONTROL METHOD
Abstract
Provided is a motor control device, including an acceleration
command calculation unit configured to calculate an acceleration
command directed to a motor, a torque command calculation unit
configured to calculate a torque command directed to the motor
based on the acceleration command and a predetermined
moment-of-inertia value, a torque correction value calculation unit
configured to estimate disturbance of the motor based on the torque
command and at least one of a motor position or a motor speed, to
thereby calculate a torque correction value for the torque command,
and a moment-of-inertia value change unit configured to change the
predetermined moment-of-inertia value based on an estimated
moment-of-inertia ratio, which is a ratio of the torque correction
value to the torque command.
Inventors: |
YOSHIURA; Yasufumi;
(Kitakyushu-shi, JP) ; KAKU; Yasuhiko;
(Kitakyushu-shi, JP) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Yaskawa Denki |
Kitakyushu-shi |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Yaskawa
Denki
|
Family ID: |
55652794 |
Appl. No.: |
15/298154 |
Filed: |
October 19, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2014/077269 |
Oct 10, 2014 |
|
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15298154 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02P 21/143 20130101;
H02P 7/00 20130101; G05B 19/404 20130101; H02P 29/10 20160201 |
International
Class: |
H02P 7/00 20060101
H02P007/00; H02P 23/14 20060101 H02P023/14 |
Claims
1. A motor control device, comprising: an acceleration command
calculation unit configured to calculate an acceleration command
directed to a motor; a torque command calculation unit configured
to calculate a torque command directed to the motor based on the
acceleration command and a predetermined moment-of-inertia value; a
torque correction value calculation unit configured to estimate
disturbance of the motor based on the torque command and at least
one of a motor position or a motor speed, to thereby calculate a
torque correction value for the torque command; and a
moment-of-inertia value change unit configured to change the
predetermined moment-of-inertia value based on an estimated
moment-of-inertia ratio, which is a ratio of the torque correction
value to the torque command.
2. The motor control device according to claim 1, wherein the
moment-of-inertia value change unit is configured to stepwise
change the predetermined moment-of-inertia value based on the
estimated moment-of-inertia ratio.
3. The motor control device according to claim 2, wherein a
threshold for the estimated moment-of-inertia ratio when the
moment-of-inertia value change unit increases the predetermined
moment-of-inertia value and a threshold for the estimated
moment-of-inertia ratio when the moment-of-inertia value change
unit decreases the predetermined moment-of-inertia value are
different from each other.
4. The motor control device according to claim 2, wherein the
moment-of-inertia value change unit is configured to change the
predetermined moment-of-inertia value based on a value acquired by
applying a low-pass filter to the estimated moment-of-inertia
ratio.
5. The motor control device according to claim 3, wherein the
moment-of-inertia value change unit is configured to change the
predetermined moment-of-inertia value based on a value acquired by
applying a low-pass filter to the estimated moment-of-inertia
ratio.
6. The motor control device according to claim 1, further
comprising: a speed command calculation unit configured to
calculate a speed command directed to the motor; and a motor speed
estimation unit configured to estimate, based on the torque command
and the motor position, an estimated motor speed to be input to the
acceleration command calculation unit.
7. The motor control device according to claim 2, further
comprising: a speed command calculation unit configured to
calculate a speed command directed to the motor; and a motor speed
estimation unit configured to estimate, based on the torque command
and the motor position, an estimated motor speed to be input to the
acceleration command calculation unit.
8. The motor control device according to claim 3, further
comprising: a speed command calculation unit configured to
calculate a speed command directed to the motor; and a motor speed
estimation unit configured to estimate, based on the torque command
and the motor position, an estimated motor speed to be input to the
acceleration command calculation unit.
9. The motor control device according to claim 4, further
comprising: a speed command calculation unit configured to
calculate a speed command directed to the motor; and a motor speed
estimation unit configured to estimate, based on the torque command
and the motor position, an estimated motor speed to be input to the
acceleration command calculation unit.
10. The motor control device according to claim 5, further
comprising: a speed command calculation unit configured to
calculate a speed command directed to the motor; and a motor speed
estimation unit configured to estimate, based on the torque command
and the motor position, an estimated motor speed to be input to the
acceleration command calculation unit.
11. A motor control device, comprising: acceleration command
calculation means for calculating an acceleration command directed
to a motor; torque command calculation means for calculating a
torque command directed to the motor based on the acceleration
command and a predetermined moment-of-inertia value; torque
correction value calculation means for estimating disturbance of
the motor based on the torque command and at least one of a motor
position or a motor speed, to thereby calculate a torque correction
value for the torque command; and moment-of-inertia value change
means for changing the predetermined moment-of-inertia value based
on an estimated moment-of-inertia ratio, which is a ratio of the
torque correction value to the torque command.
12. A motor control method, comprising: calculating an acceleration
command directed to a motor; calculating a torque command directed
to the motor based on the acceleration command and a predetermined
moment-of-inertia value; estimating disturbance of the motor based
on the torque command and at least one of a motor position or a
motor speed, thereby calculating a torque correction value for the
torque command; and changing the predetermined moment-of-inertia
value based on an estimated moment-of-inertia ratio, which is a
ratio of the torque correction value to the torque command.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present disclosure contains subject matter related to
that disclosed in Priority Patent Application under Patent
Cooperation Treaty PCT/JP2014/077269 filed in the Japan Patent
Office on Oct. 10, 2014, the entire contents of which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] Field of the Invention
[0003] The present invention relates to a motor control device and
a motor control method.
[0004] Description of the Related Art
[0005] In WO 2005/093939 A1, there is described a motor control
device including a phase compensation unit including a disturbance
observer and a phase advance filter. In WO 2005/093939 A1, there is
described such a fact that compensation is carried out for zero to
30 times of a moment-of-inertia ratio, which is a ratio between a
value of a moment of inertia used by the motor control device and a
true value thereof, to thereby stabilize a control system and
maintain a response constant regardless of a load.
SUMMARY OF THE INVENTION
[0006] According to one embodiment of the present invention, a
motor control device includes: an acceleration command calculation
unit configured to calculate an acceleration command directed to a
motor; a torque command calculation unit configured to calculate a
torque command directed to the motor based on the acceleration
command and a predetermined moment-of-inertia value; a torque
correction value calculation unit configured to estimate
disturbance of the motor based on the torque command and at least
one of a motor position or a motor speed, to thereby calculate a
torque correction value for the torque command; and a
moment-of-inertia value change unit configured to change the
predetermined moment-of-inertia value based on an estimated
moment-of-inertia ratio, which is a ratio of the torque correction
value to the torque command.
[0007] Further, according to another embodiment of the present
invention, a motor control method includes: calculating an
acceleration command directed to a motor; calculating a torque
command directed to the motor based on the acceleration command and
a predetermined moment-of-inertia value; estimating disturbance of
the motor based on the torque command and at least one of a motor
position or a motor speed, thereby calculating a torque correction
value for the torque command; and changing the predetermined
moment-of-inertia value based on an estimated moment-of-inertia
ratio, which is a ratio of the torque correction value to the
torque command.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a control block diagram for illustrating a motor
control device according to a first embodiment of the present
invention.
[0009] FIG. 2 is a diagram for illustrating, in more detail,
control blocks of the motor control device according to the first
embodiment of the present invention.
[0010] FIG. 3 is a graph for showing an example of an operation of
the motor control device according to the first embodiment of the
present invention when a value of a moment-of-inertia ratio
J.sub.P/J.sub.0 is 15.
[0011] FIG. 4 is a graph for showing an example of the operation of
the motor control device according to the related art when the
value of the moment-of-inertia ratio J.sub.P/J.sub.0 is 35.
[0012] FIG. 5 is a graph for showing an example of the operation of
the motor control device according to the first embodiment of the
present invention when the value of the moment-of-inertia ratio
J.sub.P/J.sub.0 is 35.
[0013] FIG. 6 is a graph for showing an example of the operation of
the motor control device according to the first embodiment of the
present invention when the value of the moment-of-inertia ratio
J.sub.P/J.sub.0 is 50.
[0014] FIG. 7 is a flowchart for illustrating an operation of a
moment-of-inertia value change unit 8.
[0015] FIG. 8 is a control block diagram for illustrating the motor
control device according to a second embodiment of the present
invention.
DESCRIPTION OF THE EMBODIMENTS
[0016] From a point of view of the inventors of the present
invention, in general, in order to convert an acceleration command
value into a torque command value for a motor in the motor control,
a value of the moment of inertia of the motor itself and a load
connected to the motor is necessary. When the value of the moment
of inertia is significantly different from a true value, a control
system becomes unstable. However, it is generally difficult to
accurately acquire the value of the moment of inertia, and the
value may change during drive of the motor.
[0017] To address this problem, control of carrying out an
operation of automatically acquiring the value of the moment of
inertia is well known as so-called moment-of-inertia
identification, but a special operation is necessary for the
identification in this technology, and it is also difficult to
handle change of the moment of inertia during operation. Thus, as
described before, there is proposed a technology of adding
robustness to the control system such that the control system is
stabilized even when the value of the moment of inertia is
different from the true value to a considerable degree, but an
extent of the moment-of-inertia ratio that can be compensated has
an upper limit even in this technology.
[0018] As a result of extensive study and development of easily
stabilizing the control system regardless of the moment-of-inertia
ratio in the motor control, thereby acquiring a response regardless
of the load, the inventors of the present invention have arrived at
a novel and original motor control device. In the following, a
detailed description is given of this motor control device by means
of embodiments.
[0019] FIG. 1 is a control block diagram for illustrating a motor
control device 100 according to a first embodiment of the present
invention. On this occasion, the motor control device is a device
constructed by integrating an amplifier configured to supply
electric power for operating a servomotor and an inverter, and a
control circuit configured to control a current and a voltage
output from the amplifier and the like. Currently, the control in
the motor control device is discrete control (so-called digital
control) by a digital processor in many cases, and control blocks
illustrated in FIG. 1 do not always represent electric circuits
that physically exist, and include control blocks whose functions
are achieved by software executed on the digital processor.
[0020] According to the first embodiment, the motor control device
100 is configured to input a position command u as control input,
and to output a position X of a control subject as control
output.
[0021] In the motor control device 100, the current position X of a
load 5, namely, the motor, and machine components mounted to the
motor, is subtracted from the position command u, resulting in a
deviation e at a node 1. Subsequently, the deviation e is converted
into a speed command v by a speed command calculation unit 2.
Further, the speed command v is converted into an acceleration
command a by an acceleration command calculation unit 3. Further,
the acceleration command a is multiplied by a moment-of-inertia
value J.sub.0 so as to be converted into a torque command T in a
torque command calculation unit 4.
[0022] In general motor control, this torque command T is input to
the motor/load 5, and current/voltage control is carried out by the
inverter or the like, thereby driving the motor. According to the
embodiment, a corrected torque command T.sub.r is acquired by
adding a torque correction value T.sub.c output from a torque
correction value calculation unit 6 to the torque command T. This
corrected torque command T.sub.r is input to the motor/load 5. The
torque correction value calculation unit 6 is a disturbance
observer designed as a state observer into which a model (nominal
model) receiving disturbance is built. In an example described
later, the torque correction value calculation unit 6 includes a
current loop model, an inverse system of a nominal model, and a
low-pass filter.
[0023] Moreover, a motor speed estimation unit 7 is configured to
function as a speed observer configured to estimate the motor
speed, and simultaneously serve as a phase compensator configured
to advance the phase. An acquired estimated motor speed v.sub.e is
input to the acceleration command calculation unit 3, thereby
constructing a speed feedback loop and advancing the phase in this
loop, resulting in an improvement in the phase margin and a
stabilized response.
[0024] Moreover, in the motor control device 100 according to this
embodiment, with the operations of the torque correction value
calculation unit 6 and the motor speed estimation unit 7, the
control system can be stabilized, and desired performance of
tracking the position command u can be provided, even when an
actual moment of inertia J.sub.P of the motor/load 5 and the
moment-of-inertia value J.sub.0 used in the torque command
calculation unit 4 do not accurately match each other. On this
occasion, a range of a value of a moment-of-inertia ratio
J.sub.P/J.sub.0 being a ratio of the actual moment of inertia
J.sub.P to the moment-of-inertia value J.sub.0 in which the control
system is stable and the desired tracking performance is provided,
is 0 to 30 as described in BACKGROUND OF THE INVENTION.
[0025] In the motor control device 100 according to this
embodiment, the motor speed is estimated, and the phase is
compensated by using the motor speed estimation unit 7 in the speed
feedback loop, but the phase compensation does not always need to
be carried out, and the motor speed may be directly acquired by
differentiating the current position X being the output of the
motor/load 5, in place of the estimation of the motor speed. In
this case, influence of disturbance including the mismatch between
the moment-of-inertia value J.sub.0 and the actual moment of
inertia J.sub.P tends to be exerted, and the phase margin is not
provided. Thus, the range of the value of the moment-of-inertia
ratio J.sub.P/J.sub.0 in which the control system is stable and the
desired tracking performance is provided decreases.
[0026] Further, a moment-of-inertia value change unit 8 is
provided, and is configured to change the moment-of-inertia value
J.sub.0 used in the torque command calculation unit 4 based on the
ratio between the torque correction value T.sub.c and the torque
command T, thereby stabilizing the control system and providing the
desired tracking performance regardless of the value of the actual
moment of inertia J.sub.P.
[0027] FIG. 2 is a diagram for illustrating, in more detail,
control blocks of the motor control device 100 according to the
first embodiment of the present invention. The illustrated control
blocks are examples for embodying the control blocks illustrated in
FIG. 1, and it is not intended that the control blocks illustrated
in FIG. 1 be limited to the control blocks illustrated in FIG.
2.
[0028] As illustrated, the torque command calculation unit 4 is
configured to multiply the acceleration command a by the
moment-of-inertia value J.sub.0. Moreover, a low-pass filter 41 is
inserted on a subsequent stage of the torque command calculation
unit 4.
[0029] The motor/load 5 includes a control subject including a
moment of inertia J.sub.M of the motor and a moment of inertia
J.sub.L of the load connected to the motor. On this occasion, as an
example of the control subject, a product of R(s) being a
mechanical resonance system, and 1/(J.sub.M+J.sub.L)s being a
mechanical rigid body system, is exemplified. Moreover, a current
control unit including an inverter or the like, which is configured
to convert the corrected torque command T.sub.r into a current is
provided on a preceding stage of the motor/load 5. Moreover, a
disturbance torque T.sub.d is acting on the motor/load 5, and is
described as a disturbance to the corrected torque command T.sub.r.
The moment-of-inertia value J.sub.0 used in the torque command
calculation unit 4 is ideally and preferably a moment-of-inertia
value acquired by combining the moment of inertia J.sub.M of the
motor and the moment of inertia J.sub.L of the load connected to
the motor, which are included in the control subject, but those
moments of inertia, particularly the moment of inertia J.sub.L of
the load, are difficult to be acquired in advance. Therefore, in
the motor control device 100 according to this embodiment, as an
initial value of the moment-of-inertia value J.sub.0, the value of
the moment of inertia J.sub.M of the motor or a value generally
close to the value of the moment of inertia J.sub.M of the motor is
used.
[0030] The torque correction value calculation unit 6 is the
disturbance observer configured to calculate a difference between
an estimated actual torque, which is estimated from the current
position X by using an inverse system 61 of a nominal model of the
control subject, and a command torque, which is calculated from the
corrected torque command T.sub.r by using a current loop model 62,
thereby estimating the disturbance torque. The torque correction
value calculation unit 6 is configured to output the torque
correction value T.sub.c for compensating the disturbance torque. A
low-pass filter for stabilizing an operation is appropriately used
in the torque correction value calculation unit 6. On this
occasion, the torque command T reflects the moment-of-inertia value
J.sub.0 used in the torque command calculation unit 4, and the
torque correction value T.sub.c reflects the actual moment of
inertia J. The ratio T.sub.c/T of those values is thus
approximately equal to the moment-of-inertia ratio J.sub.P/J.sub.0.
In the following, the value T.sub.c/T is referred to as estimated
moment-of-inertia ratio . The estimated actual torque may be
estimated not from the current position X, but from a motor speed
{dot over (X)}.
[0031] The motor speed estimation unit 7 is constructed as a loop
including a control subject model 71 and a low-pass filter 72, and
is configured to use the control subject model 71 to estimate the
motor speed, and to extract the estimated motor speed v.sub.e from
a preceding stage of the low-pass filter 72, thereby applying the
speed feedback advanced in phase to the acceleration command
calculation unit 3. This configuration improves the phase margin in
the speed feedback loop as described before.
[0032] When the moment-of-inertia value change unit 8 changes the
moment-of-inertia value J.sub.0 of the torque command calculation
unit 4, and the inverse system 61 of the nominal model of the
torque correction value calculation unit 6 and the control subject
model 71 of the motor speed estimation unit 7 use the
moment-of-inertia value J.sub.0, the moment-of-inertia value
J.sub.0 used in the inverse system 61 of the nominal model and the
control subject model 71 is also changed.
[0033] FIG. 3 is a graph for showing an example of the operation of
the motor control device 100 according to this embodiment when the
value of the moment-of-inertia ratio J.sub.P/J.sub.0 is 15. This
graph plots the motor speed the motor torque T.sub.M, and the
estimated moment-of-inertia ratio T.sub.c/T with respect to time t
from a top row in this order.
[0034] On the top row of FIG. 3, a speed command (time derivative
of the position command u) is indicated by the broken line, and it
is recognized that the motor speed {dot over (X)} indicated by the
solid line is provided so as to approximately track the speed
command . Moreover, as shown on a middle row of FIG. 3, the motor
torque T.sub.M presents a stable value respectively during
acceleration and deceleration. Further, as shown on a bottom row of
FIG. 3, the estimated moment-of-inertia ratio T.sub.c/T presents a
value including more or less deviations respectively during the
acceleration and the deceleration, but generally close to 15 being
the value of the moment-of-inertia J.sub.P/J.sub.0. This fact
indicates that the estimated moment-of-inertia ratio T.sub.c/T can
be used as the estimated value of the moment-of-inertia ratio
J.sub.P/J.sub.0.
[0035] In contrast, FIG. 4 is a graph for showing an example of the
operation of the motor control device according to the related art
when the value of the moment-of-inertia ratio J.sub.P/J.sub.0 is
35. The related-art motor control device used in this example is
assumed to be the same in the configuration as the motor control
device 100 except that the moment-of-inertia value change unit 8
included in the motor control device 100 according to the
embodiment is not provided.
[0036] As apparent from a top row of FIG. 4, the motor speed {dot
over (X)} fluctuates without being able to track the speed command
, and the control system has lost stability in this example. It is
apparent that the desired tracking performance is not provided in
this state. This is because the value of the moment-of-inertia
ratio J.sub.P/J.sub.0 exceeds a compensable range provided by a
disturbance observer (torque correction value calculation unit 6
according to this embodiment) and a phase compensation unit (motor
speed estimation unit 7 according to this embodiment), and the
control system no longer can track the disturbance. As shown on a
middle row of FIG. 4, the motor torque T.sub.M also fluctuates, and
a waveform is truncated due to a torque limit of the motor. As
shown on a bottom row of FIG. 4, the estimated moment-of-inertia
ratio T.sub.c/T also significantly fluctuates in the value, and the
value of the moment-of-inertia ratio J.sub.P/J.sub.0 can no longer
be estimated after the control system has lost the stability. In
FIG. 4, the scales on the vertical axes in the plots of the motor
torque T.sub.M shown on the middle row and the estimated
moment-of-inertia ratio T.sub.c/T shown on the bottom row are not
the same as those of FIG. 3.
[0037] FIG. 5 is a graph for showing an example of the operation of
the motor control device 100 according to this embodiment when the
value of the moment-of-inertia ratio J.sub.P/J.sub.0 is 35
similarly to FIG. 4. In the motor control device 100, as in the
case shown in FIG. 3, as shown on a top row of FIG. 5, the motor
speed {dot over (X)} generally tracks the speed command , and as
shown on a middle row of FIG. 5, the motor torque T.sub.M quickly
converges to stable values respectively during the acceleration and
the deceleration. Thus, it is recognized that the control system is
stable, and the desired tracking performance is provided.
[0038] On this occasion, as shown on a bottom row of FIG. 5, the
value of the estimated moment-of-inertia ratio T.sub.c/T quickly
increases simultaneously with the start of the acceleration of the
motor. On this occasion, the moment-of-inertia value change unit 8
of the motor control device 100 is configured to monitor the value
of the estimated moment-of-inertia ratio T.sub.c/T, and to stepwise
change the moment-of-inertia value J.sub.0 used by the torque
command calculation unit 4 when the value of the estimated
moment-of-inertia ratio T.sub.c/T becomes more than a predetermined
value (referred to as increase-time threshold ratio). On this
occasion, the motor control device 100 can provide the stable
control up to approximately 25 to 30 of the value of the
moment-of-inertia ratio J.sub.P/J.sub.0 estimated based on the
estimated moment-of-inertia ratio T.sub.c/T, and the increase-time
threshold ratio is thus set to 20 for allowing a margin. Moreover,
an initial value of the moment-of-inertia value J.sub.0 is the
moment of inertia J.sub.M of the motor.
[0039] As a result, J.sub.0 is J.sub.M at the start of the
acceleration of the motor, and when the estimated moment-of-inertia
ratio T.sub.c/T becomes more than 20, J.sub.M is added to J.sub.0,
and the J.sub.0 thus becomes 2J.sub.M. As a result, J.sub.0
increases by two times, and the estimated moment-of-inertia ratio
T.sub.c/T decreases by a half. Then, the estimated
moment-of-inertia ratio T.sub.c/T generally stabilizes in a
vicinity of 17.5. This corresponds to the fact that the
moment-of-inertia ratio becomes J.sub.P/2J.sub.M=17.5 after the
moment-of-inertia value J.sub.0 is updated. Below the bottom row of
FIG. 5, the moment-of-inertia value J.sub.0 is also shown.
[0040] In this way, the motor control unit 100 always maintains the
moment-of-inertia ratio J.sub.P/J.sub.0 equal to or less than 25 to
30 regardless of the value of the actual moment of inertia J.sub.P,
thereby providing the stability of the control and the desired
tracking performance.
[0041] FIG. 6 is a graph for showing an example of the operation of
the motor control device 100 according to this embodiment when the
value of the moment-of-inertia ratio J.sub.P/J.sub.0 is 50. As
shown on a top row of FIG. 6, also in this case, as in the case
shown in FIG. 3, the motor speed generally tracks the speed command
, and as shown on a middle row of FIG. 6, the motor torque T.sub.M
quickly converges to stable values respectively during the
acceleration and the deceleration. Thus, it is recognized that the
control system is stable, and the desired tracking performance is
provided.
[0042] The value of the estimated moment-of-inertia ratio T.sub.c/T
is shown on a bottom row of FIG. 6, and first increases in the
state where the moment-of-inertia value J.sub.0 is J.sub.M being
the initial value. When the value of the estimated
moment-of-inertia ratio T.sub.c/T becomes more than the
increase-time threshold ratio 20, J.sub.M is added to the
moment-of-inertia value J.sub.0 by the moment-of-inertia value
change unit 8, and J.sub.0 is thus changed to 2J.sub.M. When the
value of the estimated moment-of-inertia ratio T.sub.c/T further
increases, and again becomes more than the increase-time threshold
ratio 20, J.sub.M is similarly added to the moment-of-inertia value
J.sub.0 by the moment-of-inertia value change unit 8, and J.sub.0
is thus changed to 3J.sub.M. As a result, the value of the
estimated moment-of-inertia ratio T.sub.c/T generally stabilizes in
a vicinity of 16.7. This corresponds to the fact that the
moment-of-inertia ratio after the update becomes
J.sub.P/3J.sub.M=16.7. Below the bottom row of FIG. 6, the
moment-of-inertia value J.sub.0 is also shown.
[0043] As described before, in the motor control device 100, each
time the value of the estimated moment-of-inertia ratio T.sub.c/T
exceeds the predetermined increase-time threshold ratio, the
moment-of-inertia value J.sub.0 is stepwise changed, that is, is
stepwise increased, by the moment-of-inertia value change unit 8.
As a result, the moment-of-inertia ratio J.sub.P/J.sub.0 estimated
based on the estimated moment-of-inertia ratio T.sub.c/T can be
maintained to be equal to or less than the predetermined value.
Thus, the control system can be stabilized, and the desired
tracking performance is provided.
[0044] On this occasion, the increase-time threshold ratio can
appropriately be set depending on the margin of the
moment-of-inertia ratio J.sub.P/J.sub.0 in which the control system
is stabilized, and the initial value of the moment-of-inertia value
J.sub.0 and the step for increasing the moment-of-inertia value
J.sub.0 are arbitrary. The moment of inertia J.sub.M of the motor
is not always required to be used unlike this embodiment. The
moment-of-inertia value J.sub.0 may be increased to a constant
multiple thereof (for example, by multiplying by two).
[0045] Further, the moment-of-inertia value change unit 8 is
configured to stepwise change the moment-of-inertia value J.sub.0
based on the estimated moment-of-inertia ratio T.sub.c/T, but may
be configured to continuously change the moment-of-inertia value
J.sub.0. However, the frequent change in the moment-of-inertia
value J.sub.0 may conversely spoil the stability of the control
system, and also increase a load imposed by information processing.
Therefore, as disclosed in the embodiment, the configuration of
stepwise changing the moment-of-inertia value J.sub.0 is preferred.
Moreover, in order to reduce influence of noise, the
moment-of-inertia value change unit 8 is preferably configured to
change the moment-of-inertia value J.sub.0 based on a value
acquired by applying an arbitrary low-pass filter, i.e., a
first-order lag filter, to the value of the estimated
moment-of-inertia ratio T.sub.c/T. A time constant on this occasion
is set to such a value as to enable the tracking of a change in the
value of the estimated moment-of-inertia ratio T.sub.c/T.
[0046] Further, the moment-of-inertia value change unit 8 is
configured to only stepwise increase the moment-of-inertia value Jo
in the description given above, but may be configured to
additionally stepwise decrease the moment-of-inertia value J.sub.0.
This configuration is provided assuming a case where, for example,
the load connected to the motor is an arm for carrying a parcel or
the like, thus, the arm is accompanied by a change in the load, and
the actual value of the moment of inertia J.sub.P significantly
decreases when the arm changes from a state where the parcel is
gripped to a state where the parcel is released, resulting in an
extremely small value of the moment-of-inertia ratio
J.sub.P/J.sub.0.
[0047] Thus, the moment-of-inertia value change unit 8 may be
configured to stepwise decrease the moment-of-inertia value J.sub.0
used in the torque command calculation unit 4 when the value of the
estimated moment-of-inertia ratio T.sub.c/T becomes less than a
predetermined value (referred to as decrease-time threshold ratio).
On this occasion, the decrease-time threshold ratio is preferably
different from the increase-time threshold ratio, and is
particularly preferably sufficiently less than the increase-time
threshold ratio. This is for preventing the moment-of-inertia value
J.sub.0 from frequently repeating the increase and the decrease
when the value of the estimated moment-of-inertia ratio T.sub.c/T
fluctuates due to noise or the like, resulting in spoiling the
stability of the control system. On this occasion, the control
system is designed to be stabilized when the actual moment of
inertia J.sub.P is equal to the moment of inertia J.sub.M of the
motor (that is, in a state of no load), and, for example, 1 can
thus be selected as the decrease-time threshold ratio. In other
words, the moment-of-inertia value change unit 8 is configured to
start subtracting J.sub.M from the moment-of-inertia value J.sub.0
when the value of the estimated moment-of-inertia ratio T.sub.c/T
becomes less than 1 being the decrease-time threshold ratio, and to
repeat the subtraction until the moment-of-inertia value J.sub.0
reaches J.sub.M being the initial value.
[0048] FIG. 7 is a flowchart for illustrating an operation of the
moment-of-inertia value change unit 8 described above. When the
motor control device 100 starts the operation, in Step ST1, the
moment-of-inertia value change unit 8 first sets the predetermined
initial value, on this occasion, the moment of inertia J.sub.M of
the motor, to the moment-of-inertia value J.sub.0 used in the
torque command calculation unit 4.
[0049] Then, in Step ST2, the moment-of-inertia value change unit 8
determines whether or not the value of the estimated
moment-of-inertia ratio T.sub.c/T is more than 20, being the
increase-time threshold ratio. When the value of the estimated
moment-of-inertia ratio T.sub.c/T is more than 20, being the
increase-time threshold ratio, the moment-of-inertia value change
unit 8 proceeds to Step ST3, and adds the predetermined value,
being the moment of inertia J.sub.M of the motor on this occasion,
to the moment-of-inertia value J.sub.0, thereby stepwise increasing
the moment-of-inertia value J.sub.0.
[0050] In Step ST2, when the value of the estimated
moment-of-inertia ratio T.sub.c/T is not more than the
increase-time threshold ratio, the moment-of-inertia value change
unit 8 proceeds to Step ST4, and determines whether or not the
value of the estimated moment-of-inertia ratio T.sub.c/T is less
than 1 being the decrease-time threshold ratio . When the value of
the estimated moment-of-inertia ratio T.sub.c/T is less than 1
being the decrease-time threshold ratio, the moment-of-inertia
value change unit 8 further proceeds to Step ST5, and determines
whether or not the moment-of-inertia value J.sub.0 has already been
equal to the moment of inertia J.sub.M of the motor, which is the
predetermined initial value. When the moment-of-inertia value
J.sub.0 is not the initial value, that is, some value has been
added to the moment-of-inertia value J.sub.0, the moment-of-inertia
value change unit 8 proceeds to Step ST6, and subtracts the
predetermined value, on this occasion, the moment of inertia
J.sub.M of the motor, from the moment-of-inertia value J.sub.0,
thereby stepwise decreasing the moment-of-inertia value
J.sub.0.
[0051] In any of the case where the processing in Step ST3 is
finished, the case where the processing in Step ST6 is finished,
the case where, in Step ST4, the value of the estimated
moment-of-inertia ratio T.sub.c/T is determined not to be less than
the decrease-time threshold ratio, and in the case where, in Step
ST5, the moment-of-inertia value J.sub.0 is determined to have
already reached the predetermined initial value, the
moment-of-inertia value change unit 8 returns to Step ST2. The
moment-of-inertia value change unit 8 repeats the processing from
Step ST2 to Step ST6 at a control cycle, thereby monitoring the
value of the estimated moment-of-inertia ratio T.sub.c/T.
[0052] FIG. 8 is a control block diagram for illustrating a motor
control device 200 according to a second embodiment of the present
invention. The motor control device 200 according to this
embodiment is different from the motor control device 100 according
to the previous embodiment in that, without providing the position
feedback loop, only the speed feedback loop is provided, and the
motor speed estimation unit 7 is not provided. The motor control
device 200 is the same in the other points. Thus, like components
are denoted by like reference numerals, and a redundant description
thereof is therefore omitted.
[0053] In the motor control device 200, the speed command U is
input as the command value, and the speed deviation v.sub.e being
the difference from the motor speed {dot over (X)}, is acquired at
the node 1. The acceleration command calculation unit 3 is
configured to calculate the acceleration command a based on the
speed deviation v.sub.e. Moreover, the current position X acquired
from the motor/load 5 is converted into the motor speed {dot over
(X)} by a differentiator 9, and is fed back to the node 1.
[0054] Also in this configuration, as in the above-mentioned motor
control device 100, the moment-of-inertia value change unit 8 is
configured to stepwise change the moment-of-inertia value J.sub.0
used in the torque command calculation unit 4, thereby providing
the stability of the control and the desired tracking performance
regardless of the actual value of the moment of inertia J.sub.P.
The moment-of-inertia value J.sub.0 is changed based on the
estimated moment-of-inertia ratio T.sub.c/T also in the motor
control device 200, and the operation for the change is not
different.
[0055] The embodiments above are described as specific examples,
and the invention disclosed in this specification is not limited to
the configurations of those specific examples. Various
modifications may be made by a person skilled in the art to the
disclosed embodiments. For example, the shape, the number, the
arrangement, or the like of the physical configurations may be
changed. Moreover, the control according to the embodiments is not
limited to the control achieved in the disclosed flowchart as long
as the control employs an algorithm having an equivalent function.
It is intended that the technical scope of the invention disclosed
in this specification cover all such modifications.
[0056] In other words, it should be understood by those skilled in
the art that various modifications, combinations, sub-combinations
and alternations may occur depending on design requirements and
other factors insofar as they are within the scope of the appended
claims or the equivalents thereof.
* * * * *